西藏发现的旋齿鲨一新种

1975年珠峰登山科考队的同志们在珠穆朗玛峰以北的高寒地区工作时,采到两件有价值的脊椎动物化石标本。化石产自定日县帕卓区曲布下三迭统底部白云质灰岩中,该地海拔4880米,是已知脊椎动物化石产地中最高的地点之一。

A NEW SPECIES OF HELICOPRIONID SHARK FROM XIZANG

Among the fossils collected by the geologists associating with the .1975 Qomo-langma Mountaineering Expedition there are two specimens of a helicoprionid shark, found near Qubu in Dingri Xian (county), at an altitude of about 4880m. The fossil-bearing dolomitic limestone beds are dated on the base of ammonites and other invertebrates as of early Triassic.The two specimens, a tooth-row fragment and a preorbital part of skull evidently belong to one and the same species.The diagnostic features observed on the specimens are comparable to two genera within the fam. Helicoprionidae: Sinohelicoprion and Helicampodus. They may be summarized as follows: Teeth of cutting-type, laterally compressed and serrated anteriorly and posteriorly; lateral wing short, without differentiation into ’middle’ and ’lower’ parts; serrates on lateral wing irregular;’intermediate region without enamel covering’ almost lacking; canal on the tooth-row base shallow; spongy osteodentine layer absent; abrasion surface lacking and the base of the lateral wing truncated. The last two points are characteristic for Sinohelicoprion, a genus first established by Liu et Chang in 1963. The main differences from S. changhsingensis are: the tubular osteodentine layer of the teeth thinner than that of 8. changhsingensis so the fibrous osteodentine layer spreading into the cutting blade, the size of teeth and the whole tooth-row smaller than that of the latter.Based on the foregoing comparison we consider the new material as representing a new Sinohelicoprion species, naming it S. qomolangma.